Welcome to Anandtech wakko... one warning, this place is extremely addictive.
'G's' Are Geforce.. I dont know how to explain them technically, but they are what a pilot experiences when hes turning, or acclerating.. You get it in your car also.. Its a rating of the force thats pulling you out of your seat in a curve.. Typical People will pass out from G's of something like 6 or higher.. I think it was.. You can get G-Force suits that protect you at higher G's but I dont think many humans can handle more then 10.. (btw, you'll never get these kind of G's in a car, 5+ is in a jet)
G's force the blood from your brain down to your legs and feet, hence the passing out.